1. Field of the Invention
The present invention relates to a liquid discharge head adapted to discharge desired liquid based on the generation of bubbles, which occurs by applying thermal energy to the liquid, a liquid discharge head substrate used therefor, a manufacturing method of the liquid discharge head, a driving method of the same, and a liquid discharge apparatus equipped with the liquid discharge head. More specifically, the invention relates to a liquid discharge head having a function element made of a ferroelectric material, a liquid discharge head substrate used therefor, a manufacturing method of the liquid discharge head, a driving method of the same, and a liquid discharge apparatus equipped with the liquid discharge head.
The invention can be applied to an apparatus such as a printer, a copying machine, a facsimile having a communication system, a word processor having a printer section or the like, which is provided to perform recording on a recording medium made of paper, a string, a fiber, cloth, metal, plastic, glass, wood, ceramic or the like, and also to an industrial liquid discharge apparatus compositely combined with various processors.
In the invention, “recording” means not only the impartation of a significant image such as a character, a graph or the like to the recording medium but also the impartation of an insignificant image such as a pattern or the like thereto.
2. Related Background Art
An ink-jet recording method has conventionally been known, which performs image formation by applying energy of heat or the like to ink to cause a state change accompanied by a steep volume change of ink (generation of bubbles), discharging the ink from a discharge port by an operation force generated because of the state change, and then depositing the ink on the recording medium. As disclosed in publications such as U.S. Pat. No. 4,723,129, a recording apparatus using such a recording method typically comprises a discharge port for discharging ink, an ink flow passage communicated with the discharge port, and an electric thermal converter arranged in the ink flow passage as energy generating means to discharge ink. The recording apparatus of this kind is advantageous in that it is possible to record a high-quality image at a high speed and with low noise, in that it is possible to provide a compact and high-resolution recording apparatus, and in many other respects. Therefore, the use of such recording apparatus has become widespread in recent years, e.g., in office equipment such as a printer, a copying machine, a facsimile or the like, and even in an industrial system such as a textile printing machine or the like.
FIG. 1 shows a constitutional example of a recording head. As illustrated in FIG. 1, the liquid discharge head includes an element substrate 1 having a plurality of heaters 2 (only one is shown in FIG. 1) provided in parallel to apply thermal energy to liquid for generating bubbles, a top board 3 joined above the element substrate 1, and an orifice plate 4 joined to the front end surfaces of the element substrate 1 and the top board 3. The top board 3 has grooves, each of which is formed in a position corresponding to each heater 2. By joining the element substrate 1 and the top board 3, a liquid flow passage 7 is formed corresponding to each heater 2.
The element substrate 1 is prepared by forming a silicon oxide film or a silicon nitride film on a substrate of silicon or the like for the purpose of insulation or heat accumulation, and patterning an electric resistance layer and a wiring constituting the heater 2 thereon. The heater 2 is caused to generate heat by applying a voltage from the wiring to the electric resistance layer, and supplying a current to the electric resistance layer. On the wiring and the electric resistance layer, a protective film is formed to protect these portions from ink. Further on the protective film, a cavitation resistance film is formed to provide protection from cavitation caused by the disappearance of ink bubbles.
The top board 3 constitutes a plurality of liquid flow passages 7 and a common liquid chamber 8 provided to supply liquid to each liquid flow passage 7, and a flow passage side wall 9 is integrally provided to extend from the top portion between the heaters 2. The top board 3 is made of a silicon-based material, and can be formed by forming the patterns of the liquid flow passage 7 and the common liquid chamber 8 by means of etching, depositing a material selected from silicon nitride, silicon oxide, and so on, for the flow passage side wall 9 on the silicon substrate by a widely known film-forming method such as a CVD method or the like, and then subjecting the portion of the liquid flow passage 7 to etching.
The orifice plate 4 has a plurality of discharge ports 5 formed corresponding to the respective liquid flow passages 7 and respectively communicated with the common liquid chamber 8 via the liquid flow passages 7. The orifice plate 4 is also made of a silicon-based material, and formed by, for example shaving the silicon substrate having the discharge ports 5 to have a thickness set in the range of 10 to 150 μm. The orifice plate 4 is not always a necessary element for the invention. Thus, in place of the orifice plate 4, it is possible to provide a top board equipped with discharge ports by leaving a wall equivalent to the thickness of the orifice plate 4 in the tip surface of the top board 3 when the liquid flow passage 7 is formed in the top board 3, and forming the discharge ports in this portion.
When the heater 2 is caused to generate heat based on the foregoing arrangement, heat is applied to the liquid of a bubble generation region 10, which faces the heater 2 located in the liquid flow passage 7, and thereby bubbles are generated and grown on the heater 2 based on a film boiling phenomenon. The propagation of a pressure and the growth of the bubbles themselves based on the generation of bubbles are guided to the discharge port 5 side, and discharge from the discharge ports 5.
On the other hand, when the bubbles enter the process of disappearance, in order to compensate for the reduced volume of the bubbles in the bubble generation region 10 and for the volume of the discharged liquid, liquid is caused to flow in from an upstream side, i.e., the common liquid chamber 8 side, filling the liquid flow passage 7 again (refilling).
In addition, the described liquid discharge head includes a circuit and an element provided to drive the heater 2 and control such driving. The circuit and the element are arranged on the element substrate 1 and the top board 3 in a divided manner. The circuit and the element can be easily and finely formed by using a semiconductor wafer processing technology, as the element substrate 1 and the top board 3 are made of silicon materials.
In the recording apparatus using the foregoing head, as shown in FIG. 2, a head carriage 1001 loading the liquid discharge head and a printer body 1002 are connected to each other via a cable 1003, and recording is performed by moving the head carriage 1001 in a subscanning direction on the recording surface of the recording medium. In the case of such a structure, a wiring for supplying a current to the electric thermal converter (heater) of the liquid discharge head inevitably becomes longer. Consequently, as described above, in the case of the liquid discharge head employing ink-jet recording of the type for driving the heater by supplying a steep current thereto, a problem of easy generation of current noises occurs because of interaction of wiring inductance. In addition, when all the nozzles of the liquid discharge head are driven, a current of several amperes flows instantaneously between the head and the body, i.e., to the cable 1003, resulting in the parallel passage of a logic signal in the cable 1003. Thus, a problem of current noises being carried on a signal conductor occurs because of inductive coupling. Such current noise problems have conventionally been dealt with by loading a capacitor as a current noise countermeasure on the carriage or a relay substrate.
On the other hand, with the progress in high-density recording in recent years, the quantity of ink discharged at one time has been reduced more and more, and studies have been conducted on various mechanisms to perform stable and highly accurate liquid discharging.
An exemplary apparatus may be one, which is adapted to provide a temperature sensor in a liquid discharge head and then maintain a head temperature in a specified range according to the detection result of the sensor.
Another exemplary apparatus may be one, which is adapted to load a nonvolatile memory on a liquid discharge head, store head information regarding a liquid discharge characteristic, a head state, and so on, in the memory, and then control the driving of the head according to such information. In this case, for the memory storing the head information, an EEPROM, a flash memory or the like is used.
The electric thermal converter provided to generate energy for discharging ink can be manufactured by using a semiconductor manufacturing process. Accordingly, the recording head of the foregoing type for discharging ink by using the electric thermal converter is constructed by forming the electric thermal converter on the element substrate 1 made of a silicon substrate, and joining the top board made of a resin of polysulfone or the like, or glass thereon, the top board having grooves for forming an ink flow passage.
Another available apparatus may be one, including, in addition to the electric thermal converter on the element substrate 1, a driver for driving the electric thermal converter, a temperature sensor used when controlling the electric thermal converter according to the temperature of the head, a driving control unit thereof, and so on, which are all arranged on the element substrate 1 based on the fact that the element substrate is made of the silicon substrate (Japanese Patent Application Laid-Open No. 7-52387 or the like). The head including the driver, the temperature sensor, the driving control unit thereof, and so on, has been put to practical use, contributing to the improvement of the reliability of the recording head and the miniaturization of the apparatus.
A current noise elimination effect by the capacitor is higher toward the portion (heater) for consuming current energy. However, a large capacitor has hitherto been required because of a large capacity needed by the capacitor provided as a current noise countermeasure. Consequently, in general, a space for installing the capacitor had to be set, and the capacitor as a current noise countermeasure was provided in the carriage or the relay substrate.
To effectively eliminate current noises, it is necessary to dispose the capacitor on a portion closer to the heater, e.g., on the element substrate for the liquid discharge head. In particular, with the higher speed of the liquid discharge head and the higher density recording in recent years, the quantity of current (current for heater driving) flowing instantaneously to the head substrate has been increased more and more. In such a situation, to counter current noises, it was necessary to set large the capacity of the capacitor and dispose it in a portion closer to the heater. But no specific solutions have been available.
On the other hand, following the lower costs of the liquid discharge device in recent years, efforts have been expended to reduce costs as well for the liquid discharge head. However, because of the arrangement of the foregoing EEPROM and the nonvolatile memory such as a flash memory as separate components on the head substrate, it has been difficult to lower costs.
Lately, an attempt has been made to control a driving condition for the liquid discharge heater by disposing various sensors in the head and feeding back the detection results thereof in real time. In this case, however, because of the frequent need to write/read information from the memory, it has been difficult to deal with the higher speed of the head in recent years by the nonvolatile memory.
Furthermore, the foregoing temperature sensor installed in the element substrate was provided primarily for the purpose of measuring the temperature of the element substrate. With the higher density of the liquid discharge head in recent years, however, the effect of the state of ink itself such as a temperature, concentration or the like, or its kind on recording has been larger than the temperature of the substrate. Thus, the sensor function must have high accuracy.
FIG. 3 shows another head having a structure different from that of the foregoing head. FIG. 3 specifically shows in section the head structure along a liquid flow passage. This head (referred to as a liquid discharge head or a recording head, hereinafter) includes an element substrate 1 having a plurality of heaters 2 (only one is shown in FIG. 3) provided in parallel as discharge energy generation elements for supplying thermal energy to generate bubbles in liquid, a top board 3 joined above the element substrate 1, an orifice plate 4 joined to the front end surfaces of the element substrate 1 and the top board 3, and a movable member.
The arrangement of the element substrate 1, the top board 3, the orifice plate 4, and so on, is basically similar to that shown in FIG. 1, and thus description thereof will be omitted.
The liquid discharge head shown in FIG. 3 is provided with a cantilever-beam shaped movable member 6 disposed oppositely to the heater 2 in such a manner that the liquid flow passage 7 can be divided into a first liquid flow passage 7a communicated with the discharge port 5, and a second liquid flow passage 7b having the heater 2 as described above. The movable member 6 is a thin film made of a silicon-based material such as silicon nitride, silicon oxide or the like.
The movable member 6 is disposed away from the heater 2 by a specified distance in a position facing the heater 2 to cover the same such that a fulcrum 6a can be set in the upstream side of a large flow directed from the common liquid chamber 8 through the movable member 6 to the discharge port 5 by the discharge operation of liquid, and a free end 6b is set in a downstream side with respect to the fulcrum 6a. The bubble generation region 10 is formed between the heater 2 and the movable member 6.
With the foregoing arrangement, when the heater 2 generates heat, the heat is applied to the bubble generation region 10 between the movable member 6 and the heater 2. As a result, bubbles are generated and grown on the heater 2 because of a film boiling phenomenon. A pressure generated following the growth of the bubbles is preferentially applied to the movable member 6. Then, as indicated by a broken line in FIG. 3, the movable member 6 is displaced to open widely to the discharge port 5 side around the fulcrum 6a. Depending on the displacement of the movable member 6 or its displaced state, the propagation of the pressure or the growth of the bubbles themselves based on the generation of the bubbles is guided to the discharge port 5 side, and the liquid is discharged from the discharge port 5.
In other words, because of the arrangement of the movable member 6 having the fulcrum 6a set in the upstream side (common liquid chamber 8 side) of the flow of liquid in the liquid flow passage 7 and the free end 6b set in the downstream (discharge port 5 side), the pressure propagation direction of the bubbles is guided downstream, causing the pressure of the bubbles to make direct and efficient contribution to a discharging operation. In addition, the growth direction itself of the bubbles is guided downstream as in the case of the pressure propagation direction, and grown more greatly in the downstream side than in the upstream side. In this way, by using the movable member to control the growth direction itself of the bubbles and the pressure propagation direction thereof, it is possible to improve basic discharge characteristics including discharge efficiency, a discharge velocity, and so on.
On the other hand, when the bubbles enter the process of disappearance, the bubbles quickly disappear by interaction with the elastic force of the movable member 6, and the movable member 6 also returns to its initial position indicated by a solid line in FIG. 3 at the end. In this case, to compensate for the reduced volume of the bubbles in the bubble generation region 10 and for the volume of the discharged liquid, liquid is supplied from the upstream side, i.e., from the common liquid chamber 8, to fill the liquid flow passage 7 (refilling). This liquid refilling is carried out in an efficient, rational and stable manner following the returning movement of the movable member 6.
However, with the liquid discharge head of the described structure, it was impossible to actively displace the movable member, although the displacement thereof occurred following the growth and disappearance of the bubbles. Consequently, the displacement velocity of the movable member depended on the growth and disappearance velocities of the bubbles, resulting in the impossibility of displacing the movable member at a speed exceeding such velocities. Therefore, it was impossible to improve the responsiveness of the movable member, and accordingly impossible to achieve a high recording speed with the liquid discharge head.